The most common form of inherited human blindness is retinitis pigmentosa. a family of disorders in which photoreceptor cells of the retina progressively degenerate and disappear over a period of years. The paucity of human donor tissues at early stages of these diseases and others, such as age-related macular degeneration, has led scientists worldwide to turn to similar retinal degenerations in laboratory animals. These animal models of the human diseases have and continue to play a pivotal role in vision research on the cellular mechanisms of photoreceptor degenerations and the development of potential therapeutic measures for these diseases. Among the various species with retinal degenerations, mice and rats have been used most extensively, primarily because of the experimental advantages of short gestation time;small size;powerful genetic control in the form of several readily available retinal degeneration mutants, multiple inbred and congenic strains with genetic controls: and the potential to carry out certain embryological and genetic procedures such as the production of experimental chimeras and transgenic animals. For most therapeutic studies in the areas of neuroprotection, drug delivery, transplantation and visual prostheses, the rat is the species of choice among rodents because an intermediate-sized eye, larger than that of a mouse, is required, yet large numbers of genetically controlled animals are needed. The high costs to maintain animal colonies on individual grant budgets are beyond the means of most vision scientists, and most investigators do not have the time or expertise in mammalian genetics to develop or maintain various inbred, congenic and transgenic rat strains. Thus, the specific aims of this proposal are 1) to maintain breeding colonies of mutant rats that are appropriate for studies on various forms of inherited retinal degeneration, and 2) to distribute these animals and eye tissues to investigators who request them. These lines are 1) highly inbred Royal College of Surgeons (RCS) rats with inherited retinal dystrophy;2) three rat strains congenic with RCS that serve as genetic controls and with different eye pigmentation and rates of retinal degeneration;3) P23H mutant rhodopsin transgenic rat lines with 2 different rates of degeneration;and 4) S334ter mutant rhodopsin transgenic rat lines with 4 different rates of degeneration. The overall goal of this project is to facilitate research on retinal degenerations by producing, maintaining and distributing rat models necessary for this research. Based on past performance and the increasing use and demand for these animals (almost doubling in the past 5 years), this colony and the distribution of animals will benefit scores of vision scientists and will have a major impact on research leading to the causes, prevention and treatment of retinal degenerative diseases. More than 70 current and pending grant projects are dependent upon this Retinal Degeneration Rat Model Resource established by the National Eye Institute in 1986.